1. Field of the Invention
The present invention relates to a testing device and a testing method deciding the good or bad of an electronic device by comparing an output pattern of a signal output from the electronic device and a predetermined expectation pattern.
2. Description of Related Art
A testing device tests a device under test (DUT) that is an object of test based on a test program. The test program includes commands to be executed by the testing device and an expectation pattern to be compared with a test pattern output to each terminal of the device under test or an output pattern output from each terminal of the device under test, for each command cycle. Then, the testing device sequentially reads and executes the commands of the test program from a memory. The testing device reads the test pattern corresponding to each command from the memory, and outputs to each terminal of the device under test. As a result, the output pattern is compared with a predetermined expectation pattern to be output by the device under test.
There is known a test checking a margin of the output signal from the device under test as an embodiment of a test of the device under test. In such a test, the testing device operates the device under test while changing a parameter such as the timing in which the testing device receives the output signal from the device under test and a threshold value voltage to be used for an acquisition of the output signal, and records a pass or a fail for the test performed by each parameter value. Then, assuming that each parameter is an axis of coordinate, there is made a chart in which the passes and the fails for the test using that parameter value are plotted on the coordinate. Such a chart is referred to as Shmoo plotting.
Now, since a related patent document is not recognized, the description is omitted.
Some devices under test may have the number of cycles, which is not specified or defined, from the input of a test pattern to the output of an output pattern corresponding to the test pattern. When comparing the output pattern output from such a device under test with the expectation pattern, it is desirable that the testing device has a function (a hunting function) detecting that the device under test outputs a predetermined header pattern and comparing the output pattern of the comparison object output after a particular cycle from the header pattern with the expectation pattern.
Here, considering that the Shmoo plotting is made using the testing device having the hunting function, it is necessary to change a parameter such as the acquisition timing and the threshold value voltage when the testing device acquires the output pattern of the comparison object. However, when changing these parameters, the head pattern cannot be acquired justly, and thus it is not possible to detect match or mismatch between the output pattern and the expectation pattern.
Moreover, according to the hunting function, the timing in which an output pattern sequence is output from the device under test may be different from the timing in which an expectation pattern sequence to be compared with the output pattern sequence is read from a memory. Therefore, the expectation pattern sequence and the output pattern sequence having the different timing must be synchronized in order to compare the patterns adequately.
Moreover, some devices under test may not define the timing in which the output of the output pattern sequence is started. For this reason, there is considered a method outputting a predetermined header pattern sequence showing the top of the output pattern sequence to the device under test. That is to say, according to this method, when detecting the header pattern sequence, the testing device compares an output pattern sequence output following the header pattern with the expectation pattern sequence. However, the testing device may fail in detecting the output pattern sequence identical with the header pattern sequence on account of failures of the device under test. In this case, it was difficult to analyze a cause failed in detecting the header pattern sequence conventionally.
Moreover, a conventional testing device can specify a comparison window corresponding to a range of the output pattern and the expectation pattern that are comparing objects, in order to support failure analysis of the device under test. In other words, although the output pattern and the expectation pattern are not identical with each other when the range of each pattern is outside the comparison window, the test is continued without detecting the failure. However, in case where the testing device fails in detecting the header pattern sequence outside the range of the comparison window, it may be difficult to perform failure analysis due to the mixture of unnecessary data outside the testing object range and the comparison result of the testing object when information showing the detection failure is recorded in an error log or the like or is informed a user.